In the case of such hand pipettes, according to German Pat. No. 2,456,049, the lower receiving end of the pipette housing carries a tube in which is axially, displaceably arranged a holding ring. Locking takes place by means of a setcrew which is screwed in through the wall of the holder ring against the tube of the reception end. A setscrew locking type of pipette is also disclosed in U.S. Pat. No. 3,815,790.
The problem with which the present invention is concerned is to make superfluous the use of a tool (screw driver) in the case of a hand pipette of the type mentioned initially and, furthermore, to achieve a more dependable clamping action than is possible in the case of the use of a setscrew.
Thus, according to the present invention, there is provided a hand pipette with a piston arrangement which is forced upwardly by an elastic force, the piston of which is displaceable in a pipette tip and the piston rod of which can be displaced donwardly against the elastic force by external operation to such an extent that the piston, at the lower end of the piston stroke, is at the lower end of the pipette being provided with a holding ring through which the piston rod passes and which carries a removable pipette tip at the bottom and at the top is mounted so as to be axially displaceable and lockable, wherein the top of the holding ring carries a tube which passes through an axial bore of the lower reception end of the pipette housing and on its free upper end, in a widened space of said reception end, carries an eccentric with a related eccentric axis, the wall of said widened space of said reception end, carries an eccentric with a related eccentric axis, the wall of said widened space lying eccentrically to the axis of the pipette arrangement as a whole in such a manner that rotation of the holding ring brings about a clamping of the eccentric with the surrounding wall of said widened space.
With this construction, there is achieved a locking of the cylindrical pipette tip in the position in which it sits snugly with the piston standing in the discharge position simply by rotating the holding ring, whereby, without axial displacement, the clamping between the eccentric, on the one hand, and the eccentric wall of the widened space, on the other hand, is achieved. This mode of construction renders the use of a tool superfluous. Furthermore, by means of the clamping action of the eccentric in the widened space, a better locking is achieved than in the case of the screwing method described in German Pat. No. 2,456,049.
The cylindrical pipette tip is advantageously detactably held on the holding ring by means of a bayonet joint. The direction of rotation by means of which insertion into the bayonet joint is achieved should coincide with the direction of rotation in which the clamping of the eccentric is also achieved.
The adjustment of various pipetting volumes is advantageously accomplished by means of a known type of stepped distance piece. In a construction of this type, the piston rod is held in an inner collar and advantageously this inner collar is displaceable in a tubular stepped distance piece provided with radial steps with which there co-operates a stop pin projecting radially out of the inner collar for limiting the stroke, the steps of the distance piece limiting the upper end of the piston stroke. However, in the case of the construction described in U.S. Pat. No. 3,766,785, the steps of the distance piece limit the lower end of the piston stroke, which impairs the exactitude of the pipetting procedure.
In the construction described in this U.S. Pat. No. 3,766,785, by rotation on the upper projecting end of the the inner collar, the stop pin is coordinated with various steps of the distance piece. In order, in such a construction, to achieve a locking of the hand pipette at an adjusted pipetting volume, it is advantageous to provide on the inner collar at least one outwardly spring loaded, non-rotatable projection which engages in various inner longitudinal grooves of the distance piece, i.e., by rotating on the upper projecting end of the inner collar, on the one hand the stop pin is coordinated with various steps of the distance piece and on the other hand, the spring-loaded projection engages into an associated inner longitudinal groove of the distance piece so that during use the pipette volume remains unchanged.
According to an especially simple construction of such a spring-loaded projection, the inner collar is provided with a non-rotatable end piece on which is a non-rotatable tubular elastic body which has two elastic, oppositelylying flanges, each of which engages in a longitudinal groove. The tubular elastic body preferably comprises two spring-leaf profiles, the side edges of which are bevelled and engage in longitudinal slots of the end piece and the middle parts of which are raised in such a manner that they form the flanges. When the upper projecting end of the inner collar is rotated in order to associate the stop pin with various steps of the distance piece, then the inner collar, in the case of rotating over the end piece, takes with it the two spring-leaf profiles and these are elastically pressed together when the flanges are forced out of a longitudinal groove by the rotation; if the flanges engage into the next longitudinal groove, then the spring-leaf profiles again elastically assume their original shape.
The present invention will now be explained in more detail, with reference to the accompanying drawings.